The present invention relates to a filtration procedure for assay of colloids in an aqueous colloidal suspension and is particularly useful as a quality control technique, for example to reveal radiochemical purity of colloids radiopharmaceuticals and thereby to indicate relative quality.
Such radiocolloids, for example colloids of Technetium-99m in liquid suspension, are used for liver and spleen function studies. After injection into the patient, the suspended particles are retained in the reticuloendothelial system to permit scintiphoto study of the liver, spleen, and bone marrow. However, particles larger than 8 micrometers cause difficulty by blocking capillaries of the lung producing interferring images of the lungs on the scintiphotos. In contrast, the radiochemical contaminate pertechnetate is soluable, passes through the reticuloendothelial system, but concentrates in the stomach. Interferring images of the stomach on the scintiphotos result. Therefore, qualification of pertechnetate and the larger particles of the suspension is important in the evaluation of study results.
Prior procedures for quality assessment of colloidal suspensions and particularly of radiocolloids by size classification have been tedious, time consuming and in some instances of questionable value.
In one prior art method serial stacked polycarbonate filters have been utilized where the polycarbonate filters are possessed with capillary openings of selected diameter so that the colloidal substance larger than the opening are retained at the opening while material of smaller diameter is passed to the next filter which has smaller diameter opening. In typical practice five units are utilized having diameters, respectively of 0.8, 0.6, 0.4, 0.2 and 0.08 micrometer.
Such arrangements to classify the size of colloidal particles require significant pressure to accomplish the classification. The use of the required pressure may cause (a) rupture of the filter or leakage around the filter, or (b) breakdown or deformation of the particles so the procedure yields results of questionable value.
Another, prior art method of determining quality control of radiocolloids is by Instant Thin Layer Chromatography Silica Gel (Gelman Sciences, Ann Arbor, Mich.) developed with sodium chloride 0.9% solution in water (i.e., normal saline). That method however, differentiates only radiocolloid (including larger particles) from pertechnetate.
It will be understood that, for the foregoing applications, and equally in other applications, classification analysis of the colloidal dispersion can be extremely important.